The present invention relates to a method for making diaryliodonium polyfluoro metal or metalloid salts of the formula, EQU [(R).sub.2 I]+MF.sub.d.sup.- ( 1)
where R is a C.sub.(6-13) aryl radical selected from monovalent aromatic hydrocarbon radicals and substituted monovalent aromatic hydrocarbon, M is a metal or metalloid, for example boron, arsenic, antimony and phosphorus, and d is an integer equal to 4-6 inclusive.
Prior to the present invention, the diaryliodonium salts of formula (1) were made by the method shown by Crivello U.S. Pat. No. 3,981,897, which involved the production of an intermediate diaryliodonium bisulfate salt followed by the metathesis of such salt with a polyfluoro compound of the formula, EQU XMF.sub.d, (2)
where M and d are as previously defined and X is a positively charged ion of an element selected from hydrogen, alkali metal and alkaline earth metals.
Although the method of Crivello provides a valuable route to a wide variety of diaryliodonium salts of formula (1), the yields of the desired iodonium salt are ofter unsatisfactory and stringent reaction conditions such as maintaining the temperature of the reaction during the formation of the diaryliodonium bisulfate salt of about 0.degree. C. or below due to the exothermic nature of the reaction renders the process less economically attractive.
Neiland and Karele, Journal of Organic Chemistry, U.S.S.R. 6, 889 (1970) provide an alternate route to the preparation of certain diaryliodonium salts from the reaction of iodosobenzene diacetate and toluene sulfonic acid monohydrate to produce phenyliodoso tosylate and its further condensation with anisole. Koser and Wettach, Journal of Organic Chemistry, 45 1543 (1980) demonstrated that additional diaryliodonium tosylate salts could be made by this general procedure. We have found, however, that these diayliodonium tosylate salts can be used to initiate thermal and photochemical polymerization of a limited number of cationic polymerizable organic materials, such as certain vinyl ethers. However, these tosylate salts are found to be inactive with other types of cationically polymerizable materials, for example epoxy resins. We have further found facile metathesis of the diaryliodonium tosylate salts of Neilands and Karele, for example 4-methoxydiphenyliodonium tosylate, with the polyfluoro compounds of formula (2) results in diaryliodonium salts within the scope of formula (1) which have been found useful as both thermal and photoinitiators for a wide variety of cationically polymerizable organic materials defined more particularly in U.S. Pat. No. 4,173,551, Crivello, assigned to the same assignee as the present invention.
The present invention is based on the discovery that diaryliodonium salts of formula (1) can be made by effecting reaction between a iodoaryl compound of the formula, EQU RI, (3)
where R is as previously defined, and a peracid, and combining the resulting mixture with an organic sulfonic acid and an aryl organic or aromatic compound, defined more particularly below. The ingredients of the resulting mixture are allowed to react to produce a diaryliodonium organic sulfonic acid salt. The diaryliodonium organic sulfonic acid salt is thereafter reacted with a polyfluoro metal compound of formula (2). This procedure results in the production of diaryliodonium salts of formula (1) at significantly improved yields over the prior art, while avoiding the stringent reaction conditions often found necessary such as the low temperature requirements and long reaction times of the diaryliodonium bisulfate method.